In order to safely use batteries included in battery systems and to utilize the maximum battery performance, battery systems equipped in electric vehicles (EV), in plugin hybrid electric vehicles (PHEV), and in hybrid electric vehicles (HEV) include battery control devices that detect electric voltages, temperatures, and electric currents of the battery and that calculate battery parameters such as stets of charge (SOC) or state of health (SOH) of the battery according to the detected values.
Battery parameters such as relationships between SOC and open circuit voltage (OCV) of battery or internal resistance characteristics may vary depending on SOH or deterioration modes of battery. In order to precisely identify the battery parameters, it is necessary to detect changes in battery characteristics along with deterioration and to reflect the change when calculating the battery parameters.
Patent Literature 1 listed below describes a technique for detecting, by detecting the change rate of relationship between SOC and OCV (dOCV/dSOC) and by comparing the change rate with that of before the battery is deteriorated, changes of the relationship between SOC and OCV as the battery is deteriorated.